AcquireCredentialHandle fails with SEC_E_UNKNOWN_CREDENTIALS(0x8009030D) on win7

I'm trying to authenticate my client against a server via WDigest:

credentials.User = "reader";
credentials.UserLength = 6;
credentials.Password = "password";
credentials.PasswordLength = 8;
credentials.Domain = "Domain";
credentials.DomainLength = 6;
AcquireCredentialsHandle(NULL, "WDigest", SECPKG_CRED_OUTBOUND, NULL, &credentials, NULL, NULL, &hCred, &tsExpiry);

The last call fails with code SEC_E_UNKNOWN_CREDENTIALS(0x8009030D). If I'm not wrong the OUTBOUND credentials should be authenticated by the server so I can't understand the error.

I'm having this failure only on a windows 7 machine, on windows 10 everything works fine.

Update: the error happens only when I'm logged to the machine via ssh (cygwin). Anyone knows if this login has some kind of limitation in working with credentials or with the sspi in general?